1. Technical Field
The present invention relates to a linear measuring arrangement for measuring the relative position of two objects, having a scale, a scanning carriage for scanning a measuring graduation of the scale, and a coupling having a first and second coupling element, by which the scanning carriage is coupled to a carrier device which can be fastened to one of the two objects.
2. Background Information
Such linear measuring arrangements, described in DE 28 45 542 B1, DE 32 01 887 A1 and EP 0 459 294 B1, for example, are employed for measuring distances, as well as paths, and are used in particular in connection with processing machinery for measuring the relative movement of a tool in relation to a workpiece to be processed, in connection with coordinate-measuring machinery, and increasingly also in the semiconductor industry.
In this case a scale with a measuring graduation is used as the measuring representation, which is housed, protected against environmental effects, in a housing extending linearly in the measuring direction. The measuring graduation, which is incrementally or absolutely coded, is scanned by a scanning carriage during position measurement. To this end, the scanning carriage is linearly conducted in the measuring direction on two guide faces, which extend perpendicularly with respect to each other, and is pressed against these. This guidance has proven itself, because it is assured that a constant scanning distance between the scanning carriage, in particular the scanning plate, and the scale is maintained over the entire measurement length, which guarantees a good quality of the scanning signals. The guidance of the scanning carriage is disconnected from the guidance of the object to be measured in that a carrier device with a coupling is provided between the object to be measured and the scanning carriage and connects the scanning carriage to the carrier device rigidly in the measuring direction and resiliently transversely thereto.
In EP 0 459 294 the coupling consists of two coupling elements which contact each other. A sliding layer is provided for reducing the wear between the coupling elements contacting each other. This sliding layer is a thin sliding foil and is made, for example, of a PTFE-containing plastic material. In actual use, the coupling element in accordance with the prior art, which is fastened on the carrier device, was embodied as a steel pin, which is supported in a bore of the carrier device. Starting at the contact point, the pin was symmetrically designed. In order to bring the contact point as closely as possible to the neutral plane (fiber) of the scale, i.e. against the scale itself, the diameter of the pin was selected to be very small which, however, had a negative effect on stability.
The demands made on linear measuring arrangements become increasingly greater, greater resolution, as well as greater accuracy and reproducibility of the position measurements is constantly demanded. At the same time a compact mechanical structure is to be provided, and the linear measuring arrangement should be produced in a cost-effective manner.